We have labeled adenosine receptors in rat tissues with 3HN6cyclohexyladenosine (3HCHA) and evaluated the organ distribution and drug specificity of these binding sites throughout the body. Detectable receptor concentrations are restricted to the brain and testes. Brain displays receptor levels of 9 pmoles/g wet weight of tissue while the testes display 2 pmoles/g, with all other tissues examined showing less than detectable specific binding of 3HCHA. The receptors in these two tissues appear to possess identical pharmacologic profiles with an A1 specificity for both. No change in the total number of 3HCHA binding sites is seen in testes of rats which had been hypophysectomized 14 days prior to sacrifice. This may exclude the Leydig cells as a source of adenosine receptors in the rat testes.